Here is the list of
The Twenty Five Most Valuable Blogs.
The highest is US$170 million for Gawker Properties - which includes sites Gawker, Defamer, Jezebel, Gizmodo, Lifehacker, and Jalopnik.
There are a fair few surprises in there, for example Smashing Magazine which I think is a great blog, but valued at US$7.7 million??
But as with all these lists, the values assigned are quite subjective.